The invention relates to a process which, starting from cyclopentadiene (Cp), allows the preparation of transition metal complexes bearing monosubstituted cyclopentadienyl ligands in high yields without isolation of the intermediate stages, even on an industrial scale.
Due to the great variety of possible applications of the above mentioned transition metal complexes as catalysts in organic synthesis and, in particular, in the polymerization of olefins, the ability to efficiently prepare, in industry, sandwich complexes which are monosubstituted on the cyclopentadienyl radicals has become increasingly important.
The synthesis of such compounds is known in principle. It proceeds according to the reaction equations I and II: ##STR2## with: M=metallating agent (e.g. Na, K, alkyllithium) M'=transition metal (e.g. Fe, Ti, Zr, Hf)
X=Cl, Br, I PA1 R=alkyl, cycloalkyl, benzyl, vinyl, allyl PA1 n=2-4 PA1 M" is a transition metal (Ti, Zr, Hf, Fe, V, Cr, Sc) PA1 X' is Cl, Br, I PA1 n is the oxidation number of the transition metal PA1 a is at least 1 and a is.ltoreq.n. PA1 M' is an alkali or alkaline earth metal (provided that an alkali and an alkaline earth metal are both present) PA1 is a C.sub.1 -C.sub.30 -alkyl group, C.sub.2 -C.sub.30 -alkenyl group, C.sub.7 -C.sub.30 -alkylaryl group, C.sub.8 -C.sub.30 -alkenylaryl group, C.sub.3 -C.sub.12 -alkoxyalkyl group, C.sub.1 -C.sub.30 -fluoroalkyl group or an organo-element radical such as C.sub.1 -C.sub.6 -alkyl-tri(C.sub.1 --C.sub.10 -alkyl)silyl PA1 X is halogen such as Cl, Br or I, or --OSO.sub.2 R' (R':alkyl, p-tolyl) PA1 Me is a metallating agent (Li, Na, K, NaH, KH, alkyl-lithiums, etc. (agents known from the literature for metallating monomeric cyclopentadienes) PA1 M" is a transition metal, such as Fe, V, Cr or Sc or in particular Ti, Zr or Hf, or a mixture of such transition metals PA1 X' is Cl, Br or I, or a mixture thereof PA1 n is the oxidation number of the transition metal PA1 a is at least 1 and is .ltoreq.n, and a is the number of the groups X' which are to be substituted on the transition metal.
A disadvantage here is that the substituted cyclopentadiene (CpR) must be prepared separately, before it can be reacted further.
The yields of CpR in stage I are often only small, so that complicated removal of byproducts is needed before appropriately pure product can be obtained for a further reaction.
The ability of the monoalkylcyclopentadienyl compounds to form dimers by an intermolecular Diels-Alder reaction complicates the purification, since the monomer can only be obtained in pure form by multiple distillation and thermal retro-Diels-Alder reaction. However, only these monomers can be used for the reaction according to equation II. Due to the above mentioned tendency to dimer formation, they are not stable in storage and before use again require the effort of thermal dimer removal. (Houben-Weyl Volumen 5/1c--Methoden der Organischen Chemie, editor Eugen Muller--fourth edition (1970)--pp. 660-667; Georg Thieme Verlag, Stuttgart;--Metallocenes: Gmelin Handbuch der anorganischen Chemie--supplement to 8th edition--Volumes 10 and 11: "Zirkonium-und Hafnium-Organische Verbindungen" [Organozirconium and organohafnium compounds] p. 26 ff--Verlag Chemie, Weinheim--1973; "Chemistry of Organo-Zirconium and Hafnium Compounds", D. J. Cardin; M. F. Lappert; C. L. Raston; 1986, Ellis Horwood Limited).
Although the yields of monosubstituted cyclopentadiene derivatives according to equation I could be improved in individual cases, the compounds are obtained either in a form which is still not pure enough for the reaction according to equation II or in a solvent which is unsuitable for a reaction according to equation II and must therefore be removed beforehand, which leads to losses in yield and the above-mentioned problems of dimerization (Izv. Vyssh. Uchebn, Zaved., Khim, Khim, Tekhnol., 26(6), 759-761; CA:99:157869 g).
There is therefore particular commercial and technical interest in a process which avoids the stated disadvantages and makes possible the preparation of metallocenes which are monosubstituted on the cyclopentadiene rings in a simple reaction procedure with improved yields even on a commercial scale.